Comparison of the oxygen uptake efficiency slope and 6-minute walk test in paediatric and adult Fontan patients.

BACKGROUND

Fontan patients experience progressive declines in exercise capacity, highlighting the importance of submaximal exercise parameters for clinical evaluation.

OBJECTIVES

To evaluate the oxygen uptake efficiency slope (OUES/kg) compared to 6-minute walk test (6MWT) distance in paediatric and adult Fontan patients.

METHODS

Participants included paediatric (<18 years) and adult (≥18 years) Fontan patients and matched controls. All participants completed a treadmill CPET, and VO2peak, OUES, and related variables were recorded. 6MWT was also performed, with distance (m) recorded.

RESULTS

Thirty-one Fontan patients and 30 age- and sex-matched controls were included (paediatric: 15 vs 14, both median 12 years; adults: 16 vs 16, median 20.5 vs 20 years). Both paediatric and adult Fontan patients had significantly lower OUES/kg compared to controls (p < 0.05). 6MWT distances were significantly lower in adult patients (p < 0.05) but not in paediatric patients (p > 0.05). OUES/kg and 6MWT distance were significantly correlated with VO2peak in both groups, showing stronger correlations in adults (r = 0.884, r = 0.789, p < 0.001) than in paediatric patients (r = 0.622, r = 0.609, p < 0.05). OUES/kg discriminated between patients and controls in both age groups (AUCs = 0.724 and 0.848), while 6MWT distance did so only for adults (AUC = 0.809).

CONCLUSION

Both OUES/kg and 6MWT distance may serve as valuable indicators of submaximal exercise capacity in Fontan patients, particularly in adults when maximal CPET is not feasible. While OUES/kg demonstrated superior discriminatory ability, the 6MWT remains a simple and clinically useful tool, especially for evaluating functional capacity in adult Fontan patients. These findings emphasise the complementary value of both measures and highlight the importance of age-specific assessments in this population.